1. Field of the Invention
The present invention relates to a servo motor integral with a control apparatus used with a numerically controlled machine tool or the like, in which an amplifier, a detector and a servo motor are integrated.
2. Description of the Background Art
The conventional integration of an amplifier, a detector and a servo motor used with a numerically controlled machine tool or the like, i.e., a servo motor integral with a control apparatus, is manufactured in a process, as disclosed in Japanese Laid-Open Patent Publication No. SH060-102839. As disclosed therein, the amplifier, detector and servo motor are assembled in their respective manufacturing lines and they are then integrated and assembled onto the iron core of the servo motor in a final line.
FIG. 13 is a vertical sectional view showing a first conventional design and FIG. 14 is a system configuration diagram of that conventional design. In FIGS. 13 and 14, a servo motor section 1 has a rotor 2 wherein a rotor core consisting of a permanent magnet 4 has a required number of poles and is fixed to a rotary shaft 3. Along the shaft is an opposite-to-load side ball bearing 5 and a load side ball bearing 6, the ball bearings 5, 6 are fitted to and supported by a housing 7a of one bracket 7 and a housing 8a of another bracket 8, respectively. A stator 9 is constituted by a core 10 and a coil 11 wound around the core 10 and is fixed to a frame 12. Fitting portions 12a, 12b at the ends of the frame 12 are fitted into fitting portions 7b, 8b at the ends of the brackets 7 and 8 and secured by screws (not shown). 13 represents a flexible lead wire which is connected to the coil 11 and drawn through a hole 12c formed in the frame 12 and whose front end is connected with a plug 14.
A detector 15 is constituted by, for example, an encoder having a boss 16 which is secured to the shaft end of the rotary shaft 3 by a nut 17 and on which a rotary scale 18 is fixed. The rotary scale 18 is generally a chrome-deposited glass and is etched to form slits of a required pattern. A stationary scale 19, which has been manufactured in the same manner as the rotary scale 18, has formed thereon the required pattern and has fixed thereon a 30 to 100 .mu.m gap set from the rotary scale 18 to provide a large output change.
A light-emitting device 20 such as an LED, a plurality of light-receiving devices 21, and a U-shaped installation frame 22 are secured to the bracket 7, on which the light-emitting device 20, the stationary scale 19, the light-receiving devices 21 and a printed circuit board 23 are secured. The printed circuit board 23 is loaded with a signal processing circuit 24, connected with a plug 26 by a lead wire 25, and also is connected with the light-emitting device 20 by a lead wire 24a. It is to be understood that 27 denotes the cover of the detector 15.
The assembly includes an amplifier section 28. A chassis 29 acts as an outer wall body of the amplifier section 28. The chassis 29 is provided with fins 29a. The chassis is secured to the frame 12 of the servo motor section 1. A printed circuit board 30 is loaded with a power circuit 31 and a control circuit 32, and is supported by the chassis 29 via a spacer 33. It is to be understood that 34 designates the cover of the chassis 29, a socket 36 is used with a lead wire 35 for electrical connection of the power circuit 31 and the servo motor section 1, and a socket 38 is connected at the front end of a lead wire 37 for electrical connection of the control circuit 32 and the detector 15.
The unit has a fan motor 39, which is equipped with a blade 39a, and is secured to the bracket 7 by an installation leg 39b. A fan cover 40 forms a wind path. It should be noted that when it is not necessary to cool the servo motor section 1 and the amplifier section 28, the fan motor 39 and the fan cover 40 need not be installed. It is to be understood that 41 denotes a hold-down plate, 42 represents a locking ring, and 43 designates a preloaded spring.
As another conventional design, a servo motor integral with a control apparatus is also manufactured in a process, as disclosed in Japanese Laid-Open Patent Publication No. HEI4-210753. In that process, after the assembly of the servo motor is complete, each part of the detector is assembled in the rotary shaft direction of the bracket on the opposite-to-load side of the servo motor section and, further, each part of the amplifier is assembled thereto.
FIG. 15 is a vertical sectional view showing this second conventional design and its system configuration diagram is identical to that of FIG. 14. Referring to FIG. 15, a stator 9 consists of a core 10 and a coil 11 wound around the core 10 and having reinforcing rings 44, 45 fixed to the core 10 by welding or the like. 44a and 45a designate fitting portions of the reinforcing rings 44, 45 and the brackets 8, 7. The fitting portions 44a, 45a are fitted into fitting portions 8b, 7b at the ends of the brackets 8, 7 and secured by screws (not shown). 13 represents flexible lead wires connected to the coil 11, drawn through a hole 7c formed in the bracket 7, and connected with a printed circuit board 46.
Amplifier section 28 is provided in the axial end of the rotary shaft 3 of the detector 15. 46 and 48 designate printed circuit boards. The printed circuit board 46 is loaded with the power circuit 31 and the printed circuit board 48 is loaded with the control circuit 32, and is supported by spacer 49. It should be noted that the other arrangement is identical to that of the first conventional art shown in FIGS. 13 and 14 and will therefore not described, except that U-shaped installation frame 22 is replaced with straight installation frame 47.
Operation will now be described. When the amplifier section 28 is switched on in the first conventional design shown in FIGS. 13 and 14, the power circuit 31, the control circuit 32 and the detector 15 are set to the operation state. When an external command signal is input to the control circuit 32 at this time, the power circuit 31 switches a high voltage, which has been converted from a three-phase alternating current into a direct current, under the control of the amplified command signal, to convert it into a three-phase alternating current of required frequency, voltage and current.
This current is then supplied to the coil 11 of the stator 9 in the servo motor section 1 via the lead wires 35, 13 to generate a revolving magnetic field and also cause it to work on the permanent magnet 4 to torque the rotor 2, thereby rotating the rotary shaft 3.
Accordingly, the rotary scale 18 of the detector 15 also rotates and the light of the light emitting device 20 is transmitted and intercepted according to the slits. The transmitted light is converted into any of a variety of photocurrents by the light receiving devices 21 according to the slit patterns of the rotary scale 18 and the stationary scale 19. This photocurrent is processed by the signal processing circuit 24 for use as a detector signal.
This detector signal is then fed back to the control circuit 32 via the lead wires 25, 37 for use as a velocity/rotary position signal and is compared with the command signal to rotate the servo motor section 1 to zero a difference therebetween, whereby an external machine (not shown) is drive-controlled.
The temperature rise of the servo motor section 1, the detector 15 and the amplifier section 28, which occurs due to heat generated by the resistance loss of a current flowing in the coil 11, heat generated by the switching loss of a transistor (not shown) in the power circuit 31, and other factors, is suppressed because of a cooling wind produced by the rotation of the fan motor 39 which cools the frame 12 of the servo motor section 1, the housing of the bracket 7, and the cooling fins 29a of the chassis 29 in the amplifier section 28.
In order to assemble said servo motor integral with the control apparatus, the servo motor section 1, the amplifier section 28, and the rotary scale 18, the rotary portion of the boss 16 and stationary portions consisting of the other parts in the detector 15, pre-assembled in respective assembly lines, are gathered and assembled in a final assembly line. Finally the cover 27, the fan motor 39 and the fan cover 40 are fitted to the subassembly.
It is to be understood that the second conventional design shown in FIGS. 14 and 15 also operates in the same manner as the first conventional design and will not be described.
The conventional servo motor, integral with the control apparatus which has the amplifier section fitted integrally on the core of the servo motor, as in the first conventional design, is large in dimension at right angles to the rotary shaft direction of the servo motor section. It especially has a disadvantage in that a ballscrew direct-drive feature, having a machine table driving ballscrew passing through, cannot be used because installation space under the table cannot be provided.
Also, since the amplifier section and the servo motor section are manufactured independently, processes required for the connection with the lead wires of the servo motor section and the detector make it difficult to automate lead wire connection, and the components must be assembled in a clean room to prevent dirt from sticking to the rotary scale and stationary scale and from lodging in the gap between the rotary and stationary portions of the detector. Also, because of their complicated surfaces, the servo motor section and the amplifier section, which must clean before they are transferred to the clean room, are difficult to be cleaned, resulting in poor workability and high costs.
Further, in the servo motor cooled by the fan motor, the amplifier section is in the cooling wind path, and the cooling wind strikes against the amplifier section, increasing noise and lowering cooling efficiency.
In the servo motor having the amplifier section fitted in the rotary shaft direction of the opposite-to-load side bracket (as in the second conventional design), the long dimension in the rotary shaft direction of the servo motor section requires a larger installation floor area. Further the printed circuit boards located away from the opposite-to-load side ball bearing results in low supporting rigidity and large vibration of the printed circuit boards, whereby an electronic circuit component mounting section must be held firmly by reinforcing materials and the like.
Also, the printed circuit boards must be connected with the lead wires of the servo motor and the light emitting device. Further, there are many processes required for this connection work, and it is difficult to automate lead wire connection. Finally, the servo motor section and the amplifier section must be fully cleaned in the assembling of the rotary and stationary portions of the detector in a clean room. Naturally, since the amplifier section is not assembled as a single unit, each part must be cleaned, and evaluation cannot be made as a single unit. Hence, the workability of amplifier section fitting is low and costs are high.
Accordingly, an object of the present invention is to overcome these disadvantages by providing a servo motor, integral with a control apparatus, which is small in size and low in costs, vibration, noise and temperature rise.